1. Field of the Invention
The present invention relates generally to computer-assisted drafting (CAD) systems, and in particular, to a method, apparatus, and article of manufacture for detecting incorrectly oriented lofted solids in a solid modeling system.
2. Description of the Related Art
Over the last decade, designers have changed their fundamental approach to graphics design, moving from 2D drawing systems to 3D solid modeling systems. New software makes solid modeling technology available and affordable to virtually anyone.
Solid modeling is a technique that allows designers to create dimensionally accurate 3D solid models in 3D space represented within a computer, rather than traditional 2D drawings. 3D solid models include significantly more engineering data than 2D drawings, including the volume, bounding surfaces, and edges of a design.
With the graphics capabilities of today""s computers, these 3D solid models may be viewed and manipulated on a monitor. In addition to providing better visualization, 3D solid models may be used to automatically produce 2D drawing views, and can be shared with manufacturing applications and the like.
Some 3D solid modeling systems generate parametric feature-based models. A parametric feature-based model is comprised of intelligent features, such as holes, fillets, and chamfers. The geometry of the parametric feature-based model is defined by underlying mathematical relationships (i.e., parameters) rather than by simple unrelated dimensions, which makes them easier to modify. These systems preserve design intent and try to maintain it after every change to the model.
Moreover, these features are automatically adjusted as the model is modified. The system computes any related changes to parts of the model that are dependent on a parameter, and automatically updates the entire model when the parameter is changed. For example, a through-hole will always go completely through a specified part, even if the part""s dimensions are changed.
Lofting is a useful technique for generating complex shapes in parametric feature based solid modeling systems. Typically, the user provides the system with input in the form of a number of 2D cross-sections, in a specific order, along with parameters such as tangency conditions, take-off angles, and weight factors. The system then processes this input into a 3D sheet. If needed, this 3D sheet is covered by faces at the ends, in order to convert it into a lofted solid.
However, after the sheet is covered by faces, there is no guarantee that the lofted solid is properly oriented. It is a requirement that the lofted solid be closed, connected, regular, and have a finite positive volume. To satisfy the finite positive volume requirement, it is necessary that the face normals of all the faces covering the 3D sheet are pointing outwards, with respect to the material side of the faces. The convention used by a geometric modeler is that loops are comprised of co-edges, which are oriented so that looking along the co-edge with the face normal pointing upwards, the face is on the left.
Thus, there is a need in the art for a solid modeling system that detects incorrectly oriented loft features. In addition, there is a need in the art for a solid modeling system that corrects the face normals for any incorrect orientation.
To address the requirements described above, the present invention discloses computer-implemented solid modeling system that detects incorrect orientations of lofted solids, and then ensures that the face normals of the lofted solids are correctly oriented, so that they are pointing outwards with respect to the material side of each face.